1. Field of the Invention
The present invention relates to an oscillator arrangement, and particularly to an oscillator arrangement which is controllable in its frequency, having a control input for a frequency variation, and a transformer output whose frequency-determining oscillating circuit has, as a controllable reactive element, two varactor diodes which are connected in opposing fashion and whose capacitance substantially represents the oscillating circuit capacitance.
2. Description of the Prior Art
Oscillator arrangements of the type generally set forth above can be used for purposes of frequency modulation or demodulation. In view of the non-linear properties of varactor diodes, it is known, for example through the publication "Nachrichtetechnische Zeitschrift" 1965, Vol. 4, pp. 186-190, to use two varactor diodes connected in opposing fashion in place of a single varactor diode. The linear modulation range of the frequency variation can be additionally optimized by providing that the overall capacitance of the two varactor diodes is clipped to the least extent possible by additional capacitances, and therefore fundamentally represents the capacitive reactive element of the frequency-determining oscillating circuit of the oscillator.
If high requirements are made on the linearity of the frequency variation range, in dependence upon a control voltage, even if the described linearization measures are taken into consideration, only a relatively small linear frequency variation range of approximately .+-.3% of the generated fundamental oscillation can be achieved.
As described in the publication cited above, these difficulties can be countered by using two oscillators of very high oscillating frequencies, whose oscillating frequencies are displaced relative to one another by the amount of the desired intermediate frequency and are mixed together to form the intermediate frequency. If one of these two oscillators is frequency-modulated, and in fact in the limits governed by the linearity requirements, in this manner the modulation bandwidth can be enlarged by the quantity of the frequency conversion factor.